1. Field of the Invention
Embodiments of the invention described herein pertain to the field of rotating assemblies. More particularly, but not by way of limitation, one or more embodiments of the invention enable an apparatus, system and method for measuring straightness of components of rotating assemblies.
2. Description of the Related Art
Shafting, tubing and other elements of rotating assemblies, for example in pump, drive shaft or axle applications, are required to be straight in order to operate correctly and efficiently. Specific straightness requirements depend on the particular application. High-speed multistage pump shafting, for example, has some of the most stringent straightness requirements; such shafts are required to be almost perfectly straight, within only a 0.002-0.003 inch acceptable deviation. For example, in the case of an electric submersible pump, a 20 foot long shaft may need to be straight throughout the length of the shaft within a 0.002 inch deviation. If the shaft is not straight within the allowed parameters, it will vibrate or shake while rotating due to unbalance, causing reduced effectiveness of the pump, improper functioning of the pump or even preventing the pump from functioning entirely. A bent shaft can also damage bearings, seals and couplings in the pump assembly, and cause material fatigue and shaft misalignment.
Conventional methods for straightening the shaft of a rotating assembly in electric submersible pump applications, and other applications with stringent straightness requirements, have changed very little over the past century and make use of a dial indicator, measuring scale or ruler. A typical tooling apparatus for straightening a shaft is shown in FIG. 1. Shaft 100 is supported on work bench 110 by conventional pillars 120 and conventional bearings 130. Work bench 110 is of a known flatness. Conventional pillars 120 are attached to work bench 110 and act as intermittent support for shaft 100, such as every 2 ft. along the shaft. Conventional bearings 130 nest into conventional pillars 120, and shaft 100 is inserted into conventional bearings 130. A dial indicator 140 mounted on a base is positioned next to shaft 100. Dial indicator 140 is magnetically attached to work bench 110, such that a human operator can move dial indicator 140 along the length of shaft 100 (along conventional x-axis 160). Dial indicator 140 includes needle 150, which hangs below dial indicator 140 and touches shaft 100.
FIG. 2 describes the conventional straightening process using dial indicator 140. At step 200, shaft 100 is suspended above work bench 110 in conventional bearings 130. At step 210, dial indicator 140 is set up over the top center of shaft 100 at a known distance, as measured by a human operator, along conventional x-axis 160 of shaft 100 and locked into place. At step 220, dial indicator 140 is zeroed out to begin the evaluation process. Shaft 100 is then rotated about conventional x-axis 160 at step 230, while dial indicator 140 is monitored by a human operator for movement outside an allowable tolerance from zero, such as 0.002 inches. A human operator then determines whether there has been a deviation beyond the allowable tolerance at step 270. If during rotation dial indicator 140 does not deviate beyond the allowable tolerance as deemed by a human operator, shaft 100 is considered straight at the measured location on shaft 100 at step 240. In such instances, dial indicator 140 is then relocated an inch further down shaft 100 to the next position to be measured. If on the other hand, dial indicator 140 deviates beyond the allowable tolerance while shaft 100 is rotated (as indicated by movement of dial indicator 140), the surface of shaft 100 must be mechanically manipulated at the bent location at step 250 in order to straighten shaft 100. At step 260, dial indicator is, placed back into its previous position, re-zeroed and the previously manipulated location must be re-measured. This process is repeated as indicated at step 270 until the bent location is straight within the allowable tolerance, and also repeated along the entire length of shaft 100, as indicated at step 280, until the measurement is complete at step 290.
The conventional technique for straightening elements of rotating assemblies is exceedingly time consuming, tedious and subject to human error in positioning, zeroing and reading dial indicator 140. For example, straightening a 20 foot shaft using conventional methods may take as long as eight hours and still suffer in accuracy even after excessive man hours have been spent. In addition, wear and surface anomalies in the tooling surface, support pillars and bearings may cause further inaccuracies in the measurement and straightening process. Thus, currently available straightening techniques do not satisfactorily provide the speed or quality assurance desired in connection with the straightening of rotating assemblies, particularly those with little-to-no bend tolerance, such as those with acceptable deviations of less than about 0.005 inches and/or those with acceptable deviations of only about 0.002-0.003 inches, as are used in high speed multi-stage pumps. Therefore, there is a need for faster and more accurate ways of straightening elements of rotating assemblies, and a need for an apparatus, system and method for measuring straightness of components of rotating assemblies.